The present invention pertains generally to lampholders for receiving electric lamps, and more particularly to a family of lampholders for use with mogul-based metal halide lamps that accept only lamps having a particular base structure while rejecting all others.
The earlier metal halide lamps include a relatively centrally located arc tube situated within the confines of an outer glass bulb. These arc tubes are conventionally made of quartz or ceramic, and operate at extremely high temperatures and relatively high pressures. Under certain undesirable conditions, a system failure or internal factors will result in a safety hazard being created, whereby a violent shattering of the arc tube will send hot glass and other lamp parts into contact with the bulb glass which, in turn, will break, releasing the hot glass and lamp parts into the surrounding environment. Under such conditions, there is an obvious risk of severe personal injury, fire and/or property damage.
For this reason, normally such earlier metal halide lamps are supported within what are referred to as “enclosed” fixtures whose structure is designed to contain violently released hot glass and other lamps parts. A lens cover is used in such fixtures. In addition, significant reductions in such potential violent failures can be achieved by relamping before the rated end of the life of the lamp. Another conventional manner in which such potential violent failures is reduced includes the user's periodically turning off the lamp to permit its cooling, so that upon relighting, a non-violent or less violent lamp failure is facilitated. As further referenced herein, these earlier metal halide lamps are referred to as an “enclosed-fixture lamp”.
Recently, a new or later metal halide lamp has been developed that employs a relatively thick shroud of quartz or glass, and is situated intermediate the arc tube and the outer bulb glass such that, it the event of a violent lamp failure of the type described above, the shroud is intended to intercept and contain the hot glass and other lamp parts which would otherwise impact and possibly break the bulb glass. The intended result is a less expensive and equally safe lamp and fixture combination suitable for indoor commercial lighting applications such as offices and retail spaces, as well as other environments. Manufacturers of metal halide lamps are selling these later lamps for use in what are referred to as an “open” fixture, in which the lamp is mounted such that it is exposed during its use. As further referenced herein, these later metal halide lamps are referred to as an “open-fixture lamp”.
One particular design for the open-fixture lamp comprises a lamp having a threaded base, characterized by having an insulated extension extending from the central portion of the bottom of the lamp base, with the central contact button mounted on the distal end of the insulated extension. As further referenced herein, these metal halide lamps are referred to as an “insulated extension lamp”.
There are various means known to prevent the use of insulated extension lamps in “open” light fixtures. One means is to require, or regulate, the construction of open fixtures that use a specially-designed base that will only operate with the later or open-fixture lamps, but will not operate with the earlier or enclosed-fixture lamps. The open-fixture lamp should be differently and uniquely designed to be identified as an open-fixture lamp socket by a person installing or maintaining the light fixture. U.S. Pat. No. 5,874,800 discloses a lampholder with a mogul base having a wall structure formed around the cantilevered contact and having a wall top that defines an aperture through which the insulated extension of the lamp can pass.
There remains a need to provide improved open-fixture lampholders for open-fixture lamps, which can be easily distinguished from the enclosed-fixture lampholders, and that prevent operation of enclosed-fixture lamps therein.